Low poly mesh/Oddly sharp edges on normal map where it is supposed to be smooth
There should be some lines on the normal map: 

If you have flat faces and bake normals of round forms to them, then the edges should be visible in the normal map because the normal map needs to transform those flat planes to round smooth forms while still being mapped onto the flat faces. Normal directions should change at the edges and cannot be smooth gradients. Let's have a look at what is going on with normal directions when smooth form is mapped on a corner and then the normal directions are projected onto a flat 2d texture: 

It makes sense that we see a sudden change of values where the edges are. They should not show on the shaded models. In other words - it's normal to see lines on normal maps like these :D . There may be other issues with the baking process that cause the result not to match your expectations. the game engine may expect different format of normal maps. OpenGL and DirectX treats normal coordinates differently. Try inverting the green channel in the normal map or choose -Y instead of +Y in the baking settings for the second channel: